In computed radiography nowadays radiation images originating from exposure of an object or a patient to penetrating radiation such as X-rays are often temporarily stored in a photostimulable phosphor plate instead of an x-ray film.
A digital signal representation of a radiation image which is temporarily stored in such a photostimulable phosphor plate is obtained by scanning the plate with stimulating radiation and converting image-wise modulated light which is emitted by the plate upon stimulation into a digital signal representation.
The image-wise modulated light emitted upon stimulation is focussed for example by means of an array of microlenses onto an array of transducers converting light into an electric signal. This electric signal is finally digitized.
An example of such a read out system integrated in a cassette conveying a photo stimulable phosphor screen has been described for example in US2003/0111620 and in U.S. Pat. No. 6,642,535.
Microlenses can for example be obtained from LIMO-Lissotschenko Mikrooptik, Hauert 7, 44227 Dortmunt, Germany.
Digital radiographic images digitized by a digitizer system as described higher in which a microlens array is used, are usually calibrated and corrected for remaining periodic variation.
At present current technology is capable of producing only microlens arrays of limited width.
To be able to digitize a complete line of a typical computed radiography imaging plate several microlens arrays are assembled into a larger microlens array having a width that is large enough to digitize a line of an imaging plate of commonly used dimensions.
After application of the current calibration and correction techniques, artifacts at the position of these joints remain visible.
The origin of the joint artifacts lies in the fact that several microlens arrays are assembled into a larger array. At the joints of the microlens arrays, the glue between has a different refractive index. Hence, the paths that the emitted light follows cross the glue. This causes ghost signals in the neighboring microlens elements. To avoid this ghost effect, the edges of the microlens arrays are blackened, which causes signal loss at both ends of the joints. This effect changes dependent on the focus distance, time and temperature.
It is an aspect of the present invention to provide a method to suppress these joint artifacts to an extent that they are no longer noticeable.
Although the invention will be described with reference to a read out system using an array of microlenses, the present invention can also be applied to correct signals containing artifacts having other causes. The invention can for example be used to correct full leg-full spine images, more specifically to filter out the overlap between different sub-parts of such an image.